The combination lock has been known in Europe since at least the sixteenth century, and its origin are lost. The bolt or shackle in a combination lock has slots in it. A number of tumblers are provided with numbers or letters around the outside, and projections on the inside, which fit the slots. The rings must be lined up correctly in order for the shackle to be withdrawn. Most combination locks are designed so that the combination can be changed occasionally for security. However, changing the combination numbers of the combination lock is troublesome. It is, therefore, an object of the present invention to provide a novel combination lock which is easy to use.